Datasheet

´
=
O VCC
ON
CHARGE
C V
t
I
GATE ON
G ISS
VCC
I t
C C
V
´
= -
TPS2480
TPS2481
SLUS939B –APRIL 2010–REVISED DECEMBER 2010 www.ti.com
Alternative Inrush Designs
Gate Capacitor (dV/dt) Control
The TPS2480/81 can be configured to provide a linear dV/dt turn on characteristic. The load capacitor charging
current I
CHARGE
, is controlled by a single capacitor from the GATE terminal to ground. M1 operates as a source
follower (following the gate voltage) in this implementation. Choose a charge time, t
ON
, based on the load
capacitor, C
O
input voltage V
I
, and desired charge current. When power limiting is used (V
PROG
< V
REF
) choose
I
CHARGE
to be less than P
LIM
/V
VCC
to prevent the fault timer from starting. The fault timer starts only if power or
current limit is invoked.
(26)
Use the following equation to select the gate capacitance, C
G
. C
ISS
is the gate capacitance of M1, and I
GATE
is
the TPS2480/81 nominal gate charge current. As shown in Figure 17, a series resistor of about 1 kΩ should be
used in series with C
G
.
(27)
If neither power nor current limit faults are invoked during turn on, C
T
can be chosen for fast transient turn off
response using the M1 SOA curve. Choose the single pulse time conservatively from the M1 SOA curve using
maximum operating voltage and maximum trip current.
PROG Inrush Control
A capacitor can be connected from the PROG pin to ground to reduce the initial current step seen in Figure 12.
This method maintains a relatively fast turn-on time without the drawbacks of a gate-to-ground capacitor that
include increased short circuit response time and less predictable gate clamping.
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